Oral administration of a drug is the most convenient for the patient. Proper formulations must also meet the requirements of safety and simplicity. Depending on the properties of a drug, and the therapeutic requirements, different approaches must be taken during formulation work to obtain the required delivery profile of the drug. Thus, sparingly soluble drugs to be given once a day require other types of formulations than easily soluble drugs to be taken several times a day. The matter has been discussed extensively in the literature and comprehensive reviews can be found, e.g., Langer and Wise (Eds) “Medical applications of controlled release”, vols I and II, CRC Press Inc, Boca Raton, 1984; Robinson and Lee (Eds) “Controlled drug delivery—fundamentals and applications”, Marcel Dekker, NY 1987; Bogentoft and Sjögren, in “Towards better safety of drugs and pharmaceutical products” (Ed: Braimer), Elsevier, 1980; Sandberg “Extended-release metoprolol”, Thesis, Uppsala University, 1994.
Different formulations have different mechanisms controlling the release of the active substance. In the thesis by Sandberg 1994, extended-release (ER) formulations of different types of drugs are reviewed. It is concluded that in principle two types of ER dosage forms exist: the matrix system where the drug is mixed with the matrix material (often a polymer or a wax); and the drug reservoir system where the drug is formulated into a core (tablet or pellets) surrounded by a polymeric film. The film is then a release rate-controlling barrier determined by, e.g., its permeability, the solubility of the substance, etc.
From a flexibility point of view the formulation of a drug into small discrete units coated with a film has gained much attention. Such formulations show several interesting features, e.g., flexibility in dosage and modification of release properties, different dosage forms can be developed, dose size is adaptable to suit fixed combinations, tablets can be made divisible etc. In a number of studies it was shown that safe, simple, and convenient therapy could be achieved utilising this principle for the drug metoprolol and its salts (Ragnarsson et al, Drug Develop Ind Pharmacy 13, 1495 (1987); Sandberg et al, Eur J Clin Pharmacol 33, S3 (1988) and S9 (1988); Ragnarsson et al, Int J Pharmaceutics 79, 223 (1992); Sandberg et al, Ibid 68, 167 (1991); Sandberg et al, Pharmaceuticl Res 10, 28 (1993); Sandberg et al, Drug Invest 6, 320 (1993); Sandberg, Thesis Uppsala University, 1994). However, the pellets must have good mechanical strength. These pellets are mixed with tablet-forming excipients (Ragnarsson et al, Drug Dev Ind Pharmacy 13, 1495 (1987)) and compressed into tablets. The film coat of a pellet will thus be exposed to external forces in the manufacture of the tablet. If the mechanical strength of the film coat is too low, it may result in core material breakage during the compression process. Breakage can result in a rapid and undesired increase in the release of the drug.
The formulation of metoprolol into pellets according to the above mentioned references utilised a film coating sprayed from a solution of ethyl cellulose and hydroxypropyl methyl cellulose in an organic solvent. However, for environmental reasons it will be necessary in the near future to utilise water based film forming systems for this and other drugs to be formulated as pellet systems. Also, tablet coatings in general utilising organic solvents must for the same reasons be exchanged with water based film forming materials. Thus, much effort has been directed to find suitable water based systems for film coatings in drug delivery systems.
Latex particles in water as the dispersion medium have been known for almost half a century. These particles are polymeric colloidal particles in the 10 to 1000 nm range and have been utilised as film formers, e.g., in paints, in floor coatings, printing inks, adhesives etc. If the particle polymer has a sufficiently low glass transition temperature (Tg) when the water is evaporated, the particles can coalesce to form a film.
Water based film-forming polymer latexes for the pharmaceutical industry have been known since the early eighties when commercial dispersions more frequently appeared on the market (e.g., Aquacoat®, FMC Corp.; Eudragit® NE30D, Röhm Pharma; Kollicoat® EMM30D, BASF AG). Further development has given several other products that have been tested and reported in a number of publications (Petereit and Weisbrod, Eur J Pharmaceutics and Biopharm 47, 15 (1999); Petereit et al, Ibid, 41, 219 (1995); Amighi and Moës, STP Pharma Sci 7, 141 (1997); Bodmeier and Paeratukul, Pharm Res 11, 882 (1994); Ozturk et al, J Controlled Release 14, 203 (1990). Goodhart et al, Pharmaceutical Tech April, 64 (1984); Bodmeier and Paeratakul Int J Pharmceutics 152, 17 (1997); Bodmeier and Paeratakul Drug Develop Ind Pharmacy 20, 1517 (1994)).
From these and other studies it can be concluded that one of the more interesting dispersions, due to the low Tg of the latex polymer, is Eudragit® NE30D, which contains approximately 28.5% w/w particles of the copolymer poly(ethylacrylate-co-methylmethacrylate), and approximately 1.5% w/w of the non-ionic tenside Nonoxynol 100 (a polyoxyethylated nonylphenol) as the stabilizer. A similar dispersion as Eudragit® NE30D is Kollicoat® EMM30D (BASF AG, Ludwigshafen, Germany). However, to obtain best spraying conditions and technical appearance of the film-coated pellets, an anti-sticking agent has to be added to such dispersions as reported by Petereit and Weisbrod 1995. One such agent is a glyceryl monostearate (GMS). Several patents or patent applications utilising these principles exist: Wolff et al, WO 00/13687; Wolff et al, WO 00/13686; Nagy et al, WO 99/42087; Lee et al, WO 99/30685; Eichel et al, U.S. Pat. No. 5,529,790; Eichel U.S. Pat. No. 5,478,573; Chen, U.S. Pat. No. 5,260,068; Petereit et al, EP 403,959; disclose the use of Eudragits for the (controlled) release of different types of drugs. In those applications when anti-sticking agents have to be used, combinations of surface active molecules and talc or stearates are most common. However, for our purposes these approaches are not attractive since several problems may arise due to, e.g., the combination of non-compatible materials, large amounts of extra dispersion additives, non-reproducibility during manufacturing, etc.
Another dispersion known in the art is the new latex polymer dispersion from BASF, Kollicoat® SR30D. Kollicoat® SR30D is a dispersion which contains approximately 27% w/w polyvinylacetate, and approximately 2.7% w/w polyvinylpyrrolidone and 0.3% w/w SDS (sodium dodecylsulfate) as stabilizers. However, to be useful for coating application and film formation the polymer dispersion needs a plasticizer such as Triethyl citrate (TEC) (Kolter, K et al., Proc. Int. Symp. Controlled Release Bioact. Mater., 27, 425 (2000)). The use of the plasticizer in a film coating can have a destabilizing effect on the film, probably caused by the migration of small molecules, which can result in the film coating exhibiting a change in its properties with time.
Thus, available latex polymers when used as coating materials present two major problems: (a) sticky pellets may result, due to a low Tg, which then would need extra antisticking agents, and (b) the film may not be strong enough, due to a high Tg, to resist hard compression forces during tablet production, which then would need extra plasticizing agents.
U.S. Pat. No. 4,871,546 discloses tablet coatings comprising polymethyl methacrylate, diethyl phthalate, polyethylene glycol and polyvinyl actetate which are deposited from a solution in an organic liquid, for example methanol or methylene chloride. The polyethylene glycol acts as a plasticizer. This document does not disclose coatings that are applied using aqueous conditions.
EP 431 877 discloses enteric coatings for cimetidine comprising polymer mixtures. Enteric coatings are coatings that are insoluble at low (gastric) pH, but soluble at high (intestinal) pH. This application does not disclose the use of polymers that are water insoluble at both gastric and intestinal pH.
U.S. Pat. No. 4,975,283 discloses enteric coated aspirin. This document does not disclose the use of polymers that are water insoluble at low pH, but soluble at high pH.
U.S. Pat. No. 4,800,087 discloses the combination of Eudragit®L30D and Eudragit®NE30D as a coating to provide an immediate release tablet formulation which has taste-masking properties and is chewable. This document does not disclose the modified release formulations of the present invention.